Another company that treats its employees very well and enjoys similar success (though as it's privately held, it's not as easy to analyze) is Trader Joe's.
I've generally been impressed by Aldi's ability to maintain a quality shopping experience while maintaining such low prices. Typically in the US, bargain-type stores tend to skimp on things like cleaning, repairs, merchandising/stocking, etc. This isn't really the case with Aldi.